Solution Concentration Calculator (% and mol/dm³)

Percentage concentration (Cp) expresses the solute mass per 100 g of solution in percent. Molar concentration (Cm) expresses the number of moles of solute per 1 dm³ of solution in mol/dm³. Percentage concentration is easy to prepare in practice, while molar concentration is preferred for stoichiometric calculations and chemical reactions.

Use the formula: Cp = (mSolute / mSolution) × 100%. The solution mass is the sum of solute and solvent masses. For example, 20 g NaCl in 200 g solution: Cp = (20/200) × 100% = 10%.

Molar concentration Cm = n / V, where n is the number of moles (n = mass / molar mass) and V is the solution volume in dm³. For example, 5.85 g NaCl (molar mass 58.5 g/mol) in 1 dm³: n = 0.1 mol, Cm = 0.1 mol/dm³.

A saturated solution is one in which the maximum amount of substance has been dissolved at a given temperature and pressure. Adding more substance does not increase its concentration — the excess remains as a precipitate. For example, at 20°C the maximum NaCl concentration is about 26.3%.

Use the dilution formula: C1 × V1 = C2 × V2, where C1 and V1 are the initial concentration and volume, and C2 and V2 are the target values. For example, to get 0.1 mol/dm³ from a 1 mol/dm³ solution in 1 dm³ total volume, take 0.1 dm³ of the original and add water to 1 dm³.

Cm = (Cp × density × 10) / M, where Cp is the percentage concentration [%], density is the solution density [g/cm³] and M is the molar mass [g/mol]. The factor 10 converts units (g/cm³ × dm³ = 1000 g/L, divided by 100 for percent).

Examples: table vinegar — about 5–10% acetic acid; pharmacy hydrogen peroxide — 3% H₂O₂; physiological saline — 0.9% NaCl; disinfecting alcohol — 70–96% ethanol. These are mass-percentage or volume-percentage concentrations depending on context.

Molar mass is the mass of one mole of a substance expressed in g/mol. It equals the sum of the atomic masses of all atoms in a molecule. For NaCl: Na (22.99) + Cl (35.45) = 58.44 g/mol. Atomic masses are found in the periodic table.

Volume is used for molar concentration because it simplifies measurement with laboratory glassware (pipettes, volumetric flasks) and enables direct use in kinetics and chemical equilibrium equations, where the number of molecules per unit volume is what matters.

Concentration directly affects colligative properties: higher concentration lowers the freezing point, raises the boiling point and increases osmotic pressure. This is important for antifreeze agents, food preservation and intravenous drug administration.